Oscar Pistorius looks straight ahead as he listens to evidence being given in court in Pretoria, South Africa, Wednesday, April 16, 2014. Pistorius is charged with the murder of his girlfriend, Reeva Steenkamp, on Valentines Day in 2013. (AP Photo/Gianluigi Guercia, Pool)

PRETORIA, South Africa -- Oscar Pistorius' lawyers tried to roll back the prosecution's momentum at his murder trial Wednesday following the star athlete's shaky testimony, presenting a forensic expert who quickly found his own credentials and findings sharply questioned.

With Pistorius now back watching the proceedings from a wooden bench, the double-amputee Olympian's defence team was attempting to bolster his account that he shot girlfriend Reeva Steenkamp by mistake through a toilet door in his home, thinking she was a dangerous intruder about to attack him in the night. Pistorius faces 25 years to life in prison if convicted of premeditated murder in Steenkamp's death in the early hours of Valentine's Day last year.

But former police officer Roger Dixon, testifying for the defence, also appeared unsteady as chief prosecutor Gerrie Nel warned him that it was irresponsible to "try and be an expert" in areas he was not. Nel asserted in his cross-examination that Dixon was not an expert in light, sound, ballistics, gunshot wounds or pathology -- all areas about which he was testifying.

Dixon worked at the police forensic laboratory in Pretoria until he left the force in December 2012. He was a specialist in analyzing materials at crime scenes. He now works in the geology department at the University of Pretoria.

Nel also accused him of not answering questions directly. "For an expert you are evasive," Nel said, prompting the judge at one point to tell the energetic prosecutor to "restrain" himself.

Earlier, the judge ruled that proceedings will adjourn for more than two weeks after Thursday because a member of the prosecution team has another case to attend to. The trial will resume on May 5.

During the cross-examination, Nel showed that Dixon's findings regarding Steenkamp's gunshot wounds came from analysis of autopsy photos and from a pathologist's report because he was not present at the autopsy. He also hadn't read parts of the pathology report, Nel charged.

The prosecutor also criticized Dixon for not bringing photographs and his written reports with him and abruptly told him to bring them on Thursday.

"I said I will," Dixon snapped back.

"Good," Nel responded.

Nel ridiculed Dixon's finding about the sequence of the shots that Pistorius fired at Steenkamp through the door, testimony which contradicted that of a police ballistics expert and state pathologist Prof. Gert Saayman.

"I use the word 'finding' very loosely," Nel said wryly of Dixon's theory.

Questioned by defence lawyer Barry Roux, Dixon said he believed Steenkamp was hit in the hip and the arm in quick succession by the first two of four shots while she was standing close to the toilet door. Raising his right arm in the courtroom, Dixon indicated he believed Steenkamp may have had her right arm extended and maybe her hand on the door handle, as if she was about to open the door through which she was shot.

The defence was using his testimony to try to cast doubt on the prosecution's account that Steenkamp fled to the toilet and was hiding there during a fight with Pistorius. Nel has said that the runner intentionally shot Steenkamp through the door as she faced him and while they were arguing.

Nel mocked what he said was a suggestion by Dixon that Steenkamp was knocked backward by one of the bullets.

"It's something you see on TV," Nel said dismissively, challenging the expert to find scientific literature that showed it was possible.

Nel also pounced on Dixon's concession that an audio test that the defence conducted to compare the sounds of gunshots to those of a cricket bat hitting a wood door -- which both happened on the night of the killing -- had to be done a second time because of problems with the first.

He even asked him if he was an expert at swinging a cricket bat, a cutting reference to his hitting a bat on a wood door in the defence's audio tests at a gun range.

Dixon had also said he took part in the audio tests that showed the sounds of gunshots and of a cricket bat hitting a wood door were similar and could be confused. That is important because several neighbours have testified that they heard Steenkamp scream before shots on the fatal night, backing the prosecution's case that there was a fight before Pistorius shot his girlfriend with his 9 mm pistol.

Pistorius' defence says the witnesses are mistaking the sequence and they heard Pistorius screaming in a high-pitched voice for help before breaking the toilet door open with his bat to get to Steenkamp. When played by Pistorius' lawyers in courts, the two noises were similar.

But questioned by Nel, Dixon said the tests had to be repeated and that they were recorded and edited by a music producer who had no experience in recording gunshots.

"I have no idea on the expertise of the person who recorded the sounds," Dixon said.